CN102293649A - System and method for parallel transmission in MR imaging - Google Patents

System and method for parallel transmission in MR imaging Download PDF

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Publication number
CN102293649A
CN102293649A CN2011100788406A CN201110078840A CN102293649A CN 102293649 A CN102293649 A CN 102293649A CN 2011100788406 A CN2011100788406 A CN 2011100788406A CN 201110078840 A CN201110078840 A CN 201110078840A CN 102293649 A CN102293649 A CN 102293649A
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receiving coil
coil
transmission
detuned circuit
array
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V·阿拉加潘
F·J·L·罗布
V·塔拉奇拉
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General Electric Co
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General Electric Co
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging

Abstract

The title of the invention is system and method for parallel transmission in MR imaging. A system and method for selectively operating an array of RF receive coils (65) in a transmit mode is disclosed. The system includes an RF transmit coil (56) configured to generate an RF field that excites nuclei of a subject to generate RF resonance signals, an array of RF (65) receive coils to receive the RF resonance signals, and a detuning circuit (76) coupled to each RF receive coil (70) in the array of RF receive coils (70) that is selectively switched between a disabled and an enabled state to control a resonance and impedance of the RF receive coil (70). Each RF receive coil is caused to receive RF resonance signals when its respective detuning circuit (76) is in the disabled state and is caused to modify an amplitude and phase of the RF field generated by the RF transmit coil (56) when its respective detuning circuit is in the enabled state.

Description

The system and method that is used for MR imaging parallel transmission
Technical field
Embodiments of the invention relate generally to be used for the system and method for MR imaging, and relate more specifically to be used for optionally and, make horizontal MR magnetization have desired amplitude and phase place dynamically at the system and method for transmission mode operation RF receiving coil array with the local RF field that generates the RF field that generates with the overall transfer coil and add up.
Background technology
When the material of for example tissue suffers uniform magnetic field (polarization field B 0) time, each magnetic moment of spin (spin) is attempted to align with this polarization field in the tissue, but in their feature Larmor (Larmor) frequency with random order around its precession.If material or tissue are positioned at the x-y plane and near horizontal RF magnetic field (the exciting field B of Larmor frequency 1), square or " longitudinal magnetization " M only then align ZMay rotate or " upset " in the x-y plane to produce clean laterally magnetic moment M tAt pumping signal B 1Stop the back and launch signal, and can receive and handle this signal to form image by the excited target spin.
When utilizing these signals, adopt magnetic field gradient (G with the generation image x, G yAnd G z).Usually, the sequence by measuring period scans the zone for the treatment of imaging, and wherein these gradients change according to the concrete localization method that is using.The results set of the NMR signal that digitized and processing receive, thus use one of numerous well known reconstruction techniques to come reconstructed image.
In order to generate the high quality graphic that minimizes contrast and change of sensitivity, the uniform B of MRI application requirements 1.Be used for B 1The conventional orthogonal of field excitation drives volume coil (quadrature-driven volume coil) limited field uniformity is provided, especially when magnetic field intensity/intensity increases (for example 3T or 7T magnetic field).Therefore, generate Uniform B 1The ability of field is important for the round Realization of the potentiality that the MRI that utilizes higher field strength uses.
Recently, several different methods has been proposed with homogenization B in the RF coil design 1.A kind of homogenization B that is used for 1These class methods of field are parallel transmissions.In existing MRI system, parallel transmission is proofreaied and correct transmission B by the amplitude and the phase place of each transfer element in the control multichannel transmission array coil 1The inhomogeneities of field is called passive RF shimming (passive RF shimming) in other cases.Parallel transmission also customizes magnetization by the RF pulse of usage space customization together with gradient, thereby proofreaies and correct transmission B 1The inhomogeneities of field is called active parallel transmission (active parallel transmit) in other cases.
Yet, for realizing being used for homogenization B 1There are some defectives in the existing parallel transmission method of field purpose.For example, as mentioned above, the realization of parallel transmission requires multicomponent transmission array coil, and wherein each transfer element needs by decoupling well.For the multicomponent transmission array, need each activator box (exciter box) being used for the meticulous control of RF impulse waveform, and each RF amplifier is to be used for each element of transmission array coil.This type of multicomponent transmission array coil and associated components thereof is provided, has significantly increased the hardware cost of MRI system.
Therefore expectation has a kind of system and method, and it provides uniform B 1And do not need usually to require to be used for the multicomponent transmission array coil and the associated component of parallel transmission.
Summary of the invention
The invention provides the system and method for the local RF field that is used for selectively and dynamically adds up, make horizontal MR magnetization have desired amplitude and phase place in the RF field that transmission mode operation RF receiving coil array generates with generation and overall transfer coil.Detuned circuit (detuning circuit) is coupled to each the RF receiving coil in the RF receiving coil array, impedance and resonance that it is optionally changed between forbidding and initiate mode with control RF receiving coil optionally impel RF receiving coil array to operate in transmission or receiving mode thus.
According to an aspect of of the present present invention, in a plurality of gradient coils that a kind of MRI system comprises the main magnet that has by its hole, place around the hole of this main magnet and the hole that is arranged in main magnet and be configured to generate the RF transmission coil of RF field, wherein the nuclear of the object of placing with generation RF resonance signal in RF field excitation the hole in.This MRI system also comprises in the hole that is arranged in main magnet and with respect to the RF transmission coil places so that receive the RF receiving coil array of RF resonance signal, and the detuned circuit that is coupled to each RF receiving coil in the RF receiving coil array, described detuned circuit is optionally changed impedance and the resonance with control RF receiving coil between forbidding and initiate mode.Each RF receiving coil is impelled to receive the RF resonance signal when its corresponding detuned circuit is in the disabled status, and amplitude and the phase place of being impelled the RF field of revising the generation of RF transmission coil when its corresponding detuned circuit is in the initiate mode.
According to another aspect of the present invention, the method of a kind of MRI of being used for system parallel transmission impels whole RF transmission coil to generate a RF field during being included in the transmission cycle of MRI system operation, and impels the array of RF receiving coil to generate the RF field that second time changed during the transmission cycle of MRI system operation.The RF field of impelling RF receiving coil array to generate the variation of second time further comprises enables the detuned circuit that is coupled to RF receiving coil array, and optionally and dynamically control detuned circuit with impedance and off resonance in the control detuned circuit, also control impedance and off resonance in the RF receiving coil array thus, thereby impel RF receiving coil array during the transmission cycle of MRI system operation, to generate the RF field that second time changed.When transmission cycle is finished, this method also comprises the forbidding detuned circuit so that impel RF receiving coil array received by the object emission and RF resonance signal that generate in response to the RF field of a RF field and the variation of second time, and the RF resonance signal that storage receives on computer-readable storage medium.
According to of the present invention more on the one hand, in a plurality of gradient coils that a kind of MRI system comprises the main magnet that has by its hole, place around the hole of this main magnet and the hole that is arranged in main magnet and be configured to during the transmission cycle of MRI system, generate B 1The RF transmission coil of field, wherein B 1The nuclear of the object of placing in the field excitation hole is to generate the RF resonance signal.This MRI system also comprise in the hole that is arranged in main magnet and be positioned at the RF transmission coil around the RF receiving coil array of volume, and be coupled to RF receiving coil array and arrange with the detuned circuit that optionally impels RF receiving coil array and in one of transmission mode and receiving mode, operate.This detuned circuit is arranged and is configured to operate in initiate mode during the transmission cycle of MRI system, so that dynamically control impedance and off resonance in the RF receiving coil array, wherein detuned circuit is arranged in the local B that the operation in the initiate mode impels the generation of RF receiving coil array to have expectation amplitude and phase place 1.This detuned circuit arranges and also is configured to operate in disabled status during the receiving cycle of MRI system, and wherein the operation that is arranged in the disabled status of detuned circuit impels RF receiving coil array received in response to B 1And local B1 field and the RF resonance signal that generates.
Various further features and advantage will become apparent from the detailed description and the accompanying drawings hereinafter.
Description of drawings
What accompanying drawing illustrated present imagination is used to carry out the preferred embodiments of the present invention.
In the accompanying drawing:
Fig. 1 is the schematic block diagram in conjunction with MR imaging system of the present invention.
Fig. 2 is that wherein RF receiving coil array has the detuned circuit that is coupled to it according to the perspective view of the RF receiving coil array of relative patient's placement of one embodiment of the invention.
Fig. 3 is the sketch map of RF receiving coil that is coupled to its detuned circuit according to having of one embodiment of the invention.
Fig. 4 is the circuit diagram according to the detuned circuit of one embodiment of the invention.
The specific embodiment
With reference to Fig. 1, the primary clustering in conjunction with preferred nuclear magnetic resonance (MRI) system 10 of the embodiment of the invention is shown.By the operation of operator's control station 12 control system, operator's control station 12 comprises keyboard or other input equipment 13, control panel 14 and display screen 16.Control station 12 is communicated by letter with isolating computer system 20 by link 18, and system 20 makes the demonstration and the generation of the image of operator on can control display screen 16.Computer system 20 comprises a plurality of modules, its by backboard 20a with communicate with one another.These modules comprise image processor block 22, CPU module 24 and memory module 26, and its known in the prior art conduct is used for the frame buffer of storing image data array.Computer system 20 is controlled 32 by high speed serialization link 34 with isolating system and is communicated by letter.Input equipment 13 can comprise mouse, stick, keyboard, tracking ball, touch screen, optical wand, acoustic control or any similar or input equipment of being equal to, and can be used for mutual how much indications.
System's control 32 comprises the module collection that links together by backboard 32a.These modules comprise CPU module 36 and pulse generator module 38, and pulse generator module 38 is connected to operator's control station 12 by serial link 40.By link 40, system's control 32 receives the scanning sequence that order will be carried out with indication from the operator just.Pulse generator module 38 operating system assemblies are with the scanning sequence of carry out desired and produce data, sequential, intensity and the shape of the RF pulse that this data indication produces and the sequential and the length of data acquisition window.Pulse generator module 38 is connected to the set 42 of gradient amplifier, with sequential and the shape of indication at the gradient pulse of scan period generation.Pulse generator module 38 can also obtain controller 44 from physiology and receive patient datas, and physiology obtains controller 44 from being connected to a plurality of different sensors received signals of patient, for example from the ECG signal of the electrode that is attached to the patient.And final, pulse generator module 38 is connected to scan room interface circuit 46, the signal that it is associated with magnet system and patient's situation from various pick off receptions.Also just by scan room interface circuit 46, patient's place system 48 receives order the patient is moved to the desired locations that is used to scan.
The gradient waveform that pulse generator module 38 produces be applied to have Gx, the gradient amplifier system 42 of Gy and Gz amplifier.Each gradient amplifier excitation is used for the magnetic field gradient that space encoding is obtained signal summarily by corresponding physical gradient coil in the gradient coil assembly of 50 expressions with generation.Gradient coil assembly 50 forms the part of magnet assembly 52, it comprises polarized magnets 54 and single whole RF coil 56, and single whole RF coil 56 is used as transmission coil to generate horizontal RF magnetic field (the exciting field B in the x-y plane according to an example embodiment of the present invention 1).Transceiver module 58 in system's control 32 produces pulse, and these pulses are amplified by RF amplifier 60 and are coupled to transmission coil 56 by transmission switch 62.The consequential signal that excited target among the patient is authorized ejaculation can pass through isolating RF receiver coil array 65 (for example, the birdcage surface coil array) to be responded to, and is coupled to preamplifier 64 by transmission switch 62.The MR signal that amplifies demodulation in the receptor part of transceiver 58, filtering and digitized.Transmission switch 62 is by controlling from the signal of pulse generator module 38 during transmission mode RF amplifier 60 being electrically connected to transmission coil 56, and during receiving mode preamplifier 64 is connected to receiving coil 65.
The MR signal that receiving coil array 65 picks up is by transceiver module 58 digitizeds and be transferred to memory module 66 in the system control 32.When in memory module 66, having obtained the array of original k-spatial data, scan and finish.This original k-spatial data is re-arranged to each k-spatial data array that is used for each image of reconstruct, and each in these arrays all is input to array processor 68, the operation of this array processor with the data Fourier transform in array of image data.This view data is transported to computer system 20 by serial link 34, and image data storage is in memorizer there.In response to the order that receives from operator's control station 12, this view data can be filed in long-term storage apparatus, and perhaps it can further be handled and be transported to operator's control station 12 by image processor 22 and be presented on the display 16.
Referring now to Fig. 2,, the perspective view with respect to patient's receiving coil array 65 is shown according to one embodiment of the invention.Receiving coil array 65 is included in a plurality of independent coil part or the loop 70 that wherein has the expectation radius.Control electronic device 72 may be operably coupled to receiving coil array 65, and 72 runnings of control electronic device are with the power supply of control to array 65.The loop 70 that control electronic component 72 is coupled to array 65 via adapter 74.
Also comprise the DC circuit corresponding to each wire loop 70 in the array 65, it has and will be called the form of " active detuned circuit (active detuning circuit) " and summarily identify 76.Detuned circuit 76 be with array 65 in the tank circuit that is connected in series of respective coil loop 70, and it is controlled so that optionally revise the impedance of mobile electric current in the corresponding wire loop 70, this will explain hereinafter in more detail.That is, during transmission and receiving cycle, detuned circuit 76 can optionally be activated and forbid to reduce and to increase the impedance of mobile electric current in the corresponding wire loop 70 respectively.The layout 77 of detuned circuit 76 is provided, makes detuned circuit 76 be coupled to each wire loop 70.
Note, the typical case's " detuned circuit " who is used for receiving coil will turn round usually with at transmission cycle/impulse duration from around electromagnetic field decoupling receiving coil fully.Yet according to one embodiment of the invention, detuned circuit 76 running is with from around electromagnetic field " tuning " and " imbalance " wire loop 70 optionally.That is, when forbidding during receiving cycle during detuned circuit 76, receiving coil array 65 is as the signal of typical receiving array (that is, become Low ESR) with excited target nuclear emission in the induction patient.Yet, when during transmission cycle, enabling detuned circuit 76, receiving coil array 65 from the imbalance of overall transfer coil (promptly, receiving coil array 65 is opened or " skew " from Larmor frequency is tuning) to be used as the local transmission coil, this local transmission coil adds the B that overall transfer coil 56 (Fig. 1) generates to 1, so that the amplitude and the phase place of the inductive fields that the control transmission coil forms.Specifically, detuned circuit 76 impels detuned circuit to have inductive impedance rather than big actual impedance via its imbalance of enabling, make from overall transfer coil 56 with induction by current to receiving coil array 65.Therefore impel receiving coil array 65 as the local transmission coil, this local transmission coil generates local B 1, it revises the induced B that transmission coil 56 generates 1The amplitude and the phase place of field.Therefore, receiving coil array 56 can be called the field enhancing receiving array (FER array) that is provided for parallel transmission.
Shown in the sketch map of Fig. 3 with respect to the realization of the detuned circuit 76 of receiving coil loop 70.As shown therein, wire loop 70 comprises the tuning capacitor 78 that is connected between the coil cabling (coil trace) 80.DC control 82 is placed and be connected to detuned circuit 76 along coil cabling 80, and DC control 82 runnings are to enable/to forbid detuned circuit 76 and to control it and operate impedance and the off resonance that changes in the wire loop 70.Equally also has preposition amplification decoupling circuit 84, comprising diode 86 along what the coil cabling 80 of wire loop 70 was placed.84 runnings of preposition amplification decoupling circuit with by diode 86 respectively receive with transmission cycle during optionally preamplifier 64 (also shown in Figure 1) is connected with wire loop 70 and disconnects.
Referring now to Fig. 4,, the circuit diagram of detuned circuit 76 is shown according to an example embodiment of the present invention.Detuned circuit 76 comprises inducer 88, diode 90 (promptly, " enable diode "), variodenser (varactor) or varactor 92 and variable or step attenuator 94, attenuator 94 further comprises a plurality of high power resistors 96,98,100 and diode 102,104,106.Also comprise a plurality of DC control 108-116 in the detuned circuit 76, its running is with the operation of control diode 90, variodenser diode 92 and variable attenuator 94.Although when forming detuned circuit 76, the concrete layout of inducer 88, diode 90, variodenser diode 92 and variable attenuator 94 is shown, but should recognize that detuned circuit 76 can change aspect its definite assembly of arranging and wherein comprising, and the embodiment shown in Fig. 4 changes relatively.
In the operation of detuned circuit 76, DC control 108 runnings are used to enable and forbid the purpose of detuned circuit 76 with control diode 90.When detuned circuit 76 is in the disabled status, control diode 90 by DC control 108, so that detuned circuit 76 is operating as capacitor (that is, capacitor 78) effectively during receiving cycle.When detuned circuit 76 was disabled, therefore wire loop 70 was operating as the resonance with expectation and the typical receiving coil element (that is, operating) of impedance in receiving mode.
Yet, when detuned circuit 76 is activated during transmission cycle, control diode 90 to be provided for changing the impedance and the off resonance (as the function of electric capacity) of receiving coil loop 70 by DC control 108, make it possible to control receiving coil loop 70 to generate local B 1Field (that is, in transmission mode, operating).When detuned circuit 76 during the transmission cycle/phase place of MRI system (promptly, between transmission coil 56 transmission periods by Fig. 1) when being activated, inducer 88 is converted in parallel with tuning capacitor 78, this makes tuning capacitor 78 and inducer 88 form the tank circuit of high impedance, and the electric current that is used for " prevention " wire loop 70 flows.In addition, DC control 110 runnings are with control variodenser diode 92, so that control the off resonance of detuned circuit 76 by changing its electric capacity.And, the resistance that DC control 112,114,116 runnings increase or reduce in the attenuator 94 with the operation by optionally controlling diode 102,104,106 so that via resistor 96,98,100, thus the operation of variable attenuator 94 controlled.Via the control of 112,114,116 pairs of attenuators 94 of the DC control Q factor of control group by the various combination that adds resistor 96,98,100 thus.The local B that receiving coil loop 70 generates 1The amplitude and the phase place of field can be controlled via the Selective Control of detuned circuit 76 thus, thereby make the B that generates by to transmission coil 56 1Local B is added in the field 1, and with the induced B that forms by transmission coil 56 (Fig. 1) of mode disturbance of expectation 1.
The final B that generates via the mutual of overall transfer coil 56 and receiving coil array 65 1The field will depend on the stack from the secondary field and the incident transmission coil 56 of the receiving coil array 65 in the imbalance state.According to example as described below, suppose that the incident magnetic field that transmission coil 56 generates is B i(its can linearly or polarized circlewise), wherein B 1Usually under 50 μ T.
For the wire loop 70 of receiving coil array 65, the voltage that generates along its girth will be:
E emf = - ∂ ∂ t ∫ Σ B i dS (equation 1),
Wherein dS represents infinitesimal of ∑ surface, loop.
Be known that magnetic field is frequency dependence,
Figure BSA00000463396700092
And pass through ω 0=2 π f 0, be r for radius 0 Loop coil loop 70, we can be write as equation 1:
E emf = jπ r 0 2 ω 0 B i 0 ne - jωt (equation 2)
Wherein n is for wire loop 70 normals to a surface (normal).
If wire loop 70 has common prevention impedance Z l, then the electric current that generates in this loop will be:
I l = E emf Z l = j π r 0 2 ω 0 B i 0 n Z l e - jωt (equation 3)
On the axis of centres (for example, the x axle) of wire loop 70, magnetic field can simple write become:
B x , center = μ 0 2 r 0 2 ( r 0 2 + x 2 ) 3 / 2 I l (equation 4)
Total value from the total magnetic field of equation 3 and equation 4 will be subsequently:
B tot = B i 0 + j μ 0 2 πr 0 2 ω 0 B i 0 n Z l r 0 2 ( r 0 2 + x 2 ) 3 / 2 (equation 5)
Factor is resolved in the in-field that transmission coil 56 generates, and we can have on to the normal of coil:
B tot = B i 0 n ( 1 + j μ 0 2 πr 0 2 ω 0 Z l r 0 2 ( r 0 2 + x 2 ) 3 / 2 ) (equation 6)
The field that we can define subsequently as the function of the degree of depth strengthens function (FEF), and this defines according to following formula:
f ( x ) = μ 0 2 πr 0 4 ω 0 ( r 0 2 + x 2 ) 3 / 2 (equation 7)
Its midfield strengthens function representation and multiply by the sensitivity of receiving coil loop 70 of its surface area and the product between the system frequency, and to strengthen a function be that unit measures with resistance.
Therefore, equation 6 will become:
B tot = B i 0 n ( 1 + j f ( x ) Z l ) (equation 8)
The impedance of wire loop 70 comprises real number resistive loss and imaginary part.If we will separate the blocked impedance (that is, the intrinsic resistance of load and cabling) in receiver coil loop 70 from the impedance of detuned circuit 76, wherein pass through the real part and the imaginary part (R of the blocked impedance in receiver coil loop 70 lAnd jX l) and the real part and the imaginary part (R of the controllable impedance by detuned circuit 76 Bl(t) and X Bl(t)) define Z l, then:
B tot ( x , t ) = B i 0 n ( 1 + j f ( x ) R l + R bl ( t ) + j X bl ( t ) ) (equation 9)
Thereby introduced the parametric t that representative time changes.The intrinsic impedance of receiver coil and load depends on resistance R l, resistance R lSize with wire loop 70 increases.Usually, it for each from childhood and big element can between 10 and 30 ohm, change.Equation 9 illustrates by being detuned circuit 76 appropriate reality and the Virtual Functions selected, and people can revise the original B that transmission coil 56 generates in phase place and amplitude 1.
According to embodiments of the invention, recognize that receiving coil array 65 can control via detuned circuit 76, with the active parallel transmission that is provided for passive RF shimming type transmission (that is passive parallel transmission) or has gradient.In order to use receiving coil array 65 to be used for passive parallel transmission, the off resonance between with the whole coil transmission period in the detuned circuit 76 will be set in certain fixing point, rather than dynamically change.For example, can fix the electric capacity (Fig. 4) of variodenser diode 92 by controlling 110, and make receiving coil array 65 be used for passive parallel transmission via DC.In order to use receiving coil array 65 to be used for active parallel transmission, the off resonance in the detuned circuit 76 will be dynamically controlled between with the whole coil transmission period.For example, dynamically change the electric capacity (Fig. 4) of variodenser diode 92 by controlling 110, and make receiving coil array 65 can be used for active parallel transmission via DC.
Therefore, according to embodiments of the invention, during the transmission phase place/cycle of MR sequence, receiving coil array 65 not from around the electromagnetic field decoupling, but control by detuned circuit 76, so that aggregate source is transmitted the power of coil 56 certainly in controlled way, thereby can greatly improve magnetization reversal.
Useful is via the impedance in the detuned circuit 76 control receiving coil arrays 65, to cause not having the array of coupled problem between coil.That is, each wire loop 70 has high relatively impedance in transmission during the phase place, make from the field of a wire loop can not be on another wire loop faradic current.And, because these impedances in the receiving coil array 65 (for example are subjected to the DC signal, from DC control 108-116) control, depend on quality such as variodenser diode 92 in the detuned circuit 76 and variable attenuator 94, can obtain the high fidelity on the induction field.
In receiving coil array 65, comprise detuned circuit 76 and be provided for parallel transmission in the MRI system 10, all revise the original B that transmission coil 56 generates in phase place and the amplitude during the transmission phase place/cycle of MR sequence because array 65 is operated to be created on as the local transmission coil 1The local B of field 1.B 1The realization of this modification of field is shaping RF impulse waveform in the MHz scope not, but comes induced of shaping by impedance and the off resonance that changes receiving coil arrays 65 via detuned circuit 76.The needs that this has eliminated each activator box and each RF amplifier (they must be used to the parallel transmission with multicomponent transmission array coil usually) have significantly reduced the hardware cost of MRI system thus when still being provided for parallel transmission.
The technical contribution of disclosure system and method is that it is provided for dynamically controlling via detuned circuit the impedance and the off resonance of RF receiving coil array.Detuned circuit is provided for the selectivity operation of RF receiving coil array in transmission mode to generate the local RF field of revising the RF field that is generated by the overall transfer coil, makes it possible to form the RF field with expectation amplitude and phase place.
Therefore, according to one embodiment of the present of invention, in a plurality of gradient coils that a kind of MRI system comprises the main magnet that has by its hole, place around the hole of this main magnet and the hole that is arranged in main magnet and be configured to generate the RF transmission coil of RF field, wherein the nuclear of the object of placing with generation RF resonance signal in RF field excitation the hole in.This MRI system also comprises in the hole that is arranged in main magnet and with respect to the RF transmission coil places so that receive the RF receiving coil array of RF resonance signal, and the detuned circuit that is coupled to each RF receiving coil in the RF receiving coil array, described detuned circuit is optionally changed impedance and the resonance with control RF receiving coil between forbidding and initiate mode.Each RF receiving coil is impelled to receive the RF resonance signal when its corresponding detuned circuit is in the disabled status, and amplitude and the phase place of being impelled the RF field of revising the generation of RF transmission coil when its corresponding detuned circuit is in the initiate mode.
According to another embodiment of the present invention, the method of a kind of MRI of being used for system parallel transmission impels whole RF transmission coil to generate a RF field during being included in the transmission cycle of MRI system operation, and impels the array of RF receiving coil to generate the RF field that second time changed during the transmission cycle of MRI system operation.The RF field of impelling RF receiving coil array to generate the variation of second time further comprises enables the detuned circuit that is coupled to RF receiving coil array, and optionally and dynamically control detuned circuit with impedance and off resonance in the control detuned circuit, also control impedance and off resonance in the RF receiving coil array thus, thereby impel RF receiving coil array during the transmission cycle of MRI system operation, to generate the RF field that second time changed.When transmission cycle is finished, this method also comprises the forbidding detuned circuit so that impel RF receiving coil array received by the object emission and RF resonance signal that generate in response to the RF field of a RF field and the variation of second time, and the RF resonance signal that storage receives on computer-readable storage medium.
According to an embodiment more of the present invention, in a plurality of gradient coils that a kind of MRI system comprises the main magnet that has by its hole, place around the hole of this main magnet and the hole that is arranged in main magnet and be configured to during the transmission cycle of MRI system, generate B 1The RF transmission coil of field, wherein B 1The nuclear of the object of placing in the field excitation hole is to generate the RF resonance signal.This MRI system also comprise in the hole that is arranged in main magnet and be positioned at the RF transmission coil around the RF receiving coil array of volume, and be coupled to RF receiving coil array and arrange with the detuned circuit that optionally impels RF receiving coil array and in one of transmission mode and receiving mode, operate.This detuned circuit is arranged and is configured to operate in initiate mode during the transmission cycle of MRI system, so that dynamically control impedance and off resonance in the RF receiving coil array, wherein detuned circuit is arranged in the local B that the operation in the initiate mode impels the generation of RF receiving coil array to have expectation amplitude and phase place 1.This detuned circuit arranges and also is configured to operate in disabled status during the receiving cycle of MRI system, and wherein the operation that is arranged in the disabled status of detuned circuit impels RF receiving coil array received in response to B 1And local B1 field and the RF resonance signal that generates.
This written description usage example comes open the present invention, comprises optimal mode, and makes any technical staff of this area can put into practice the present invention, comprises manufacturing and uses any device or system, and carry out any bonded method.The patentable scope of the present invention is defined by claim, and can comprise other example that those skilled in the art can expect.If this type of other example has and the indiscriminate structural element of the literal language of claim, if or they comprise having and the immaterial different equivalent structure key element of the literal language of claim, then they are intended to be positioned at the scope of claim.
The primitive part tabulation
?10 The MRI system
?12 Operator's control station
?13 Keyboard or other input equipment
?14 Control panel
?16 Display screen
?18 Link
?20 Computer system
?20a Backboard
?22 Image processor block
?24 The CPU module
?26 Memory module
?32 System's control
?32a Backboard
?34 High speed serialization link
?36 The CPU module
?38 Pulse generator module
?40 Serial link
?42 The set of gradient amplifier
?44 Physiology obtains controller
?46 The scan room interface circuit
?48 Patient's place system
?50 The gradient coil assembly
?52 The magnet assembly
?54 Polarized magnets
?56 Whole RF coil
?58 Transceiver module
60 The RF amplifier
62 The transmission switch
64 Preamplifier
65 The RF receiver coil array
66 Memory module
68 Array processor
70 Coil part
72 The control electronic device
74 Adapter
76 Detuned circuit
77 Coil part is arranged
78 Tuning capacitor
80 The coil cabling
82 DC control
84 Preposition amplification decoupling circuit
86 Diode
88 Inducer
90 Diode
92 Variodenser or varactor
94 Variable or step attenuator
96 High power resistor
98 High power resistor
100 High power resistor
102 Diode
104 Diode
106 Diode
108 DC control
110 DC control
112 DC control
114 DC control
116 DC control

Claims (10)

1. a MRI system (10) comprising:
Main magnet (54) has the hole by it;
A plurality of gradient coils (50) are placed around the described hole of described main magnet (54);
RF transmission coil (56) is arranged in the described hole of described main magnet (54) and is configured to generate the RF field, and the nuclear of the object of placing in the described hole of described RF field excitation is to generate the RF resonance signal;
The array of RF receiving coil (65) is arranged in the described hole of described main magnet (54) and with respect to described RF transmission coil (56) and places so that receive described RF resonance signal; And
Detuned circuit (76), be coupled in the array (65) of described RF receiving coil each RF receiving coil (70) and optionally between forbidding and initiate mode conversion to control the impedance and the resonance of described RF receiving coil (70);
Wherein, each RF receiving coil (70) is impelled reception RF resonance signal when its corresponding detuned circuit (76) is in described disabled status; And
Wherein, each RF receiving coil (70) is impelled the amplitude and the phase place of the described RF field of revising described RF transmission coil (56) generation when its corresponding detuned circuit (76) is in described initiate mode.
2. MRI system as claimed in claim 1 (10), wherein said detuned circuit (76) is in the described disabled status during the receiving phase of described MRI system operation, and is in the described initiate mode during the transmission phase place of described MRI system (10) operation.
3. MRI system as claimed in claim 1 (10), wherein each detuned circuit (76) is configured to make corresponding RF receiving coil (70) imbalance to have inductive impedance with in described initiate mode the time, make in described corresponding RF receiving coil (70), to induce electric current, so that impel described corresponding RF receiving coil (70) to generate local RF field by described RF transmission coil (56).
4. MRI system as claimed in claim 3 (10), wherein the local RF field that is generated by each the RF receiving coil (70) in the array (65) of described RF receiving coil is added the RF field that described RF transmission coil (56) generates to.
5. MRI system as claimed in claim 1 (10), wherein each detuned circuit (76) is configured to optionally be provided for passive parallel transmission and active parallel transmission state for its corresponding RF receiving coil (70), wherein said detuned circuit (76) is the fixedly off resonance value that passive parallel transmission is provided for its corresponding RF receiving coil (70), and dynamically adjusts the off resonance value that is used for its corresponding RF receiving coil (70) for active parallel transmission.
6. MRI system as claimed in claim 1 (10), wherein said detuned circuit (76) comprising:
Diode (90) is configured to enable and forbids described detuned circuit (76);
Variodenser diode (92) is revised the electric capacity in the described detuned circuit (76), controls the resonance of described detuned circuit (76) thus;
Variable attenuator (94) is controlled the impedance in the described detuned circuit (76); And
DC control system (108-116) is configured to generate the DC signal to control each in described diode (90), described variodenser diode (92) and the described variable attenuator (94).
7. MRI system as claimed in claim 6 (10), wherein said variable attenuator (94) comprising:
A plurality of resistors (96-100); And
Respective resistors placement in parallel in a plurality of diodes (102-106), each in wherein said a plurality of diodes (102-106) and described a plurality of resistors (96-100);
Wherein said DC control system (108-116) is optionally controlled each in described a plurality of diode (102-106) so that control the impedance of described variable attenuator (94).
8. MRI system as claimed in claim 1 (10), wherein said detuned circuit (76) is configured to dynamically control when transmitting when described RF transmission coil (56) impedance of described RF receiving coil (70).
9. MRI system as claimed in claim 1 (10), wherein said detuned circuit (76) is in being in described initiate mode the time, impels impedance in its corresponding RF receiving coil (70) to have coupled amplitude between coil between a plurality of RF receiving coils (70) in the array (65) that stops described RF receiving coil.
10. MRI system as claimed in claim 1 (10), wherein when described detuned circuit (76) was in the described initiate mode, the array (65) of described RF transmission coil (56) and described RF receiving coil formed the parallel transmission coil and arranges.
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